Code Diff Checker

Compare two pieces of code to see added, removed, and modified lines.

Original Code

New Code

See exactly what changed between two versions of code

Code Diff Checker takes an original block of code and a new block, then lists every line in a single unified view. Lines only in the new version are marked with a plus and shown in green, lines only in the original are marked with a minus and shown in red, and lines present in both appear in grey. It gives you the gist of an edit without needing Git, an IDE or a command-line tool.

Running a diff

Paste the older text into Original Code and the updated text into New Code.
Press Sample to load a tiny example pair if you want to see the output style first. Clear empties both boxes.
Press Process Now. If both boxes are empty you will be asked to enter code.
Check the summary row for the Added, Removed and Unchanged counts, then read through the marked lines.
Use Copy or Download to keep the diff as result.txt.

Editing the New Code box clears the previous result, so run Process Now again after each change.

How the algorithm behaves

The comparison walks through both versions at once. When two lines match exactly, they are reported as unchanged. When they do not, the tool looks up to five lines ahead in the new version to see whether the current original line appears there; if it does, the lines in between are treated as insertions. Otherwise the original line is reported as removed. A modified line therefore appears as a red minus line followed by its green plus replacement. Matching is exact, so a difference in indentation or a trailing space counts as a change.

Where it is useful

Reviewing a snippet a colleague sent back before pasting it into your project.
Confirming what a copy-pasted fix actually changed compared with your original function.
Comparing two versions of a stylesheet or configuration file that live outside version control.
Checking that a formatter or minifier altered only what you expected.

Things to bear in mind

This is a straightforward line-by-line method, not the more sophisticated algorithm Git uses. Blocks of more than five inserted lines, or lines that were moved to a different place in the file, may be shown as a mix of removals and additions instead of one clean move. For huge files or formal reviews, a dedicated version-control tool is more reliable. The tool is best for short and medium snippets where you want a quick, readable answer to the question of what changed.

Related Tools

Frequently Asked Questions

What do the plus and minus signs mean?

A plus line, shown in green, exists only in the new code. A minus line, shown in red, exists only in the original. Grey lines without a sign are identical in both versions. A changed line appears as a minus line followed by a plus line.

Does it detect moved lines?

No. It does not track a line that has moved elsewhere. A moved line typically shows as a removal in its old position and an addition in its new one, and large moves may make the output look noisy.

Why are whitespace-only changes shown as differences?

Lines are compared exactly, character for character. Different indentation, trailing spaces or tabs versus spaces make two lines unequal. If you only care about the code itself, tidy both versions to use the same formatting before comparing.

How is this different from the Code Compare Tool?

The Code Compare Tool pairs lines by position and shows two panels side by side, so one inserted line misaligns everything after it. The Diff Checker produces one unified list and looks ahead to recognise inserted and removed lines, which suits edits that change line counts.

Can I save the diff output?

Yes. Copy places the diff text on your clipboard, and Download saves it as a plain text file named result.txt. The saved text contains the plus and minus markers but not the red and green colours.